The present invention relates generally to polycyclic aromatic compounds that have one or more bay regions and more specifically to a process for transforming such polycyclic aromatic compounds into safe aromatic oils that have a low mutagenicity (MI) and good physical and chemical properties for safe industrial use including as rubber processing oils and inks.
Heavy Vacuum Gas Oils (HVGO's) that are not processed beyond distillation often contain a measurable proportion of polycyclic aromatic compounds (PACs). A subset of these compounds are classified as carcinogens by Environmental Protection Agency (EPA). A common trait of these carcinogenic PAC's is that they contain bay regions: concave exterior regions formed by three or more phenyl rings that are in a nonlinear arrangement.
FIG. 1 depicts examples of PAC's that have one or more bay regions.
When carcinogenic PAC's enter the body of humans or mammals, the bay regions of aromatic compounds form reactive epoxy-diol intermediates which react with the enzyme system responsible for oxidative metabolism. This reactive intermediate binds with DNA adducts and interrupts normal cell reproduction. A test developed to predict cell mutation is called the Modified Ames test and is used to determine the mutagenicity (MI), i.e. the ability to cause mutation in genetic material.
Historically HVGO's have been relied upon for their ability to provide excellent solvency for the rubber and ink oil industry; however, the use of HVGO's is currently undesirable due to the high carcinogenicity and mutagenicity of the 4-6 member fused aromatics with bay regions.
Many countries require unprocessed HVGO's to include warning labels on Safety Data Sheets to make workers aware of the danger of these compounds due to workplace exposure. The petroleum industry responded to these labeling requirements by further processing of HVGO's to extract PAC's using solvent extraction or converting the PAC's to naphthenic compounds using hydrotreating above 800 psi. These hydrotreatments removed sulfur, nitrogen, and oxygen heterocycling of PAC's. Hydrotreating also saturates the aromatic fused rings with hydrogen making the oils non-carcinogenic and non-mutagenic. These hydrotreated naphthenic oils were deemed safe for worker exposure. However these hydrotreated naphthenic oils lost significant solvency that is required in many of the applications such as rubber processing oils and inks.
The resulting hydrotreated product is a naphthenic oil with low aromaticity (10-25%) and a decrease in performance in the industry. The industry compensates for this decrease in performance by relying on the use of other additives.
In the European Union HVGO's are aggressively extracted with dimethyl sulfoxide (DMSO) to make a product called Treated Distillate Aromatic Extract (TDAE). This process results in an oil with ˜25% aromaticity. Several drawbacks to this process are an immediate yield loss of at least 15%, costly solvent usage and/or solvent recovery, extra processing and equipment costs, and the hazardous disposal of highly carcinogenic organic waste.
The alkylation of HVGO compounds with t-butyl chloride/AlCl3 or an olefin such as pentene with a zeolite catalyst can reduce the MI to less that 1 is discussed in U.S. Pat. Nos. 5,488,193 and 6,010,617 to Mackerer et al. This work was performed on a small scale (100 mg PAH) using carbon disulfide (CS2) as a reaction solvent with a suitable alkylation catalyst. No isolation route was investigated. This process was never developed for commercial use.
The alkylation of aromatics proceeds through the formation of the carbonium ion. Reaction of the carbonium with an aromatic forms the arenium ion which then loses a hydrogen as follows:Olefin+Acid→E+ (Carbonium or Carbocation)E++Ar—H→[E-Ar—H]+ (Arenium)[E-Ar—H]+—H→E-Ar